Mechanisms of land rainfall anomalies associated with tropical Atlantic variability Seek mechanisms for SST to land impacts examined by e.g., Hastenrath.

Mechanisms of land rainfall anomalies Mechanisms of land rainfall anomalies associated with tropical Atlantic variabilityassociated with tropical Atlantic variability

• Seek mechanisms for SST to land impacts examined by e.g., Hastenrath and Heller 1977, Moura & Shukla, 1981; …Enfield, 1996; … Saravanan & Chang 2000, Paegle & Mo, 2002; here focus on S. Trop. Atlantic impacts on NE Brazil • Intermediate atm/land model QTCM simulations; moist static energy diagnostics; intervention experiments, used on other teleconnection pbs. (e.g. Su and Neelin 2002, 2003)

Climate Systems Interactions group (CSI) http://www.atmos.ucla.edu/~csi

J. David Neelin and Hui Su,U.C.L.A

NCEP BrazilNCEP BrazilPrecip vs. SSTPrecip vs. SST

•SST regression on Brazil rainfall index (box)•NCEP precip (MAM)•nino3.4 effects removed•1982-98; K/(mm/day)•90% confidence stippled

•NCEP precip regression on S. Atl. SST (30S - 5N) MAM•nino3.4 effects removed•(mm/day)/K•90% confidence stippled

See also Paegle & Mo 2002

SST on Northern SST on Northern Nordeste Brazil PrecipNordeste Brazil Precip

•TAGA QTCM (MAM)•95% confidence shaded •1950-2000 ensemble of 10•(K/(mm/day))

•GOGA QTCM (MAM)•nino3.4 effects removed•90% confidence shaded •1950-2000 ensemble of 10

SST regression on Brazil rainfall index (box)

See also Saravanan & Chang 2000

Precip. regression on S. Precip. regression on S. Atl SST (30S-5N) MAMAtl SST (30S-5N) MAM

•TAGA QTCM• (90%) confidence stippled• 1982-98 ensemble of 10

•GOGA QTCM• nino3.4 effects removed• (90%) confidence stippled• 1982-98 ensemble of 10• (mm/day)/K

CMAP Precip regression on S. Atl. SST (30S-5N) MAM

• nino3.4 linear effects removed• 90% confidence stippled• 1982-98• (mm/day)/K

NCEP regression on S. NCEP regression on S. Atl. SST (30S-5N) MAMAtl. SST (30S-5N) MAM•Temperature (1000-

200mb avg) • nino3.4 effects removed• 90% confidence stippled• 1982-98• (K/K)

•Moisture (1000-850 mb avg) • nino3.4 effects removed• 90% confidence stippled• 1982-98• (g/kg)/K

Obs SST/GOGA Ts regression on S. Atl. SST index(30S-5n) MAM

• nino3.4 linear effects removed • 90% confidence stippled• 1982-98• (K/K)

GOGA QTCM GOGA QTCM regression on regression on

S. Atl. SST (30S-5N) S. Atl. SST (30S-5N) •Tropospheric temp. (1000-200 mb avg) •nino3.4 effects removed•90% confidence stippled•(K/K)

•Moisture (vert. avg)•nino3.4 effects removed•90% confidence stippled•1982-98 ensemble of 10•(g/kg)/K

GOGA (vGOGA (v··q)q)´ regression on S. Atl. SST (30S-5N) MAM regression on S. Atl. SST (30S-5N) MAM

• nino3.4 effects removed• 90% confidence stippled• 1982-98 ensemble of 10• (W/m2)

TAGA QTCM temperature (1000-200 mb avg) regression TAGA QTCM temperature (1000-200 mb avg) regression on S. Atl. SST (30S-5N) MAMon S. Atl. SST (30S-5N) MAM

• 90% confidence stippled• 1982-98 ensemble of 10• (K/K)

S. Atl. SST (30S-5N) S. Atl. SST (30S-5N) STAGA STAGA

(MAM98) – Clim(MAM98) – Clim

•Obs SST/QTCM Ts

• (K)

•QTCM Precip.• ensemble of 10• (mm/day)

STAGASTAGA(MAM98) - Clim(MAM98) - Clim

•Temperature (1000-200 mb avg) anom.

• (K)

•Moisture (vert. avg) anom.• (g/kg)

STAGASTAGAQTCM anomaliesQTCM anomalies(MAM98) - Clim(MAM98) - Clim

•Moisture advection v·q (vert. avg)• contour 3 W/m2

•Moisture convergence by divergent wind component Mq·v (vert. avg)• contour 20 W/m2

STAGA Prec – Clim STAGA Prec – Clim MAM98MAM98

•Control Precip. anom.• (mm/day)

•Experiment testing importance of advection: (v·q) anomalies suppressed• Precip. anom. • (mm/day)

S. Trop. Atl. SST on northeastern Brazil rain: S. Trop. Atl. SST on northeastern Brazil rain: Hypothesized mechanismHypothesized mechanism

• Warm SST higher moisture over ocean

• Advection raises moisture over downwind land [little effect where convectively stable]

• In & near clim. convection zone, (v·q)´, incr. P´ slightly. Main effect: balanced by moist static energy divergence M·v´. Implies low level moisture convergence Mq·v´ so

P´ =(Mq/M + 1) (v·q)´

• Mq/M large amplifies effect of (v·q)´

Paegle and Mo (2002)Paegle and Mo (2002)

DJF Precip. (merged Hulme/Xie-Arkin data) Correlation between seasonal

mean SSTAs and RPC1,2 for DJF

Correlation between SSTAs and RPC2

for SON and MAM

Saravanan & Chang (2000), [1]Saravanan & Chang (2000), [1]

• Regression Obs SST on Nino-3 (C)• Correlation higher in west• See also Enfield & Mayer (1997)

Saravanan & Chang Saravanan & Chang (2000), [2](2000), [2]

•CCM3 AGCM with obs SST 1950-1994• Squared correlation of SST to

Northern Nordeste Brazil precipitation index (box) (11-3S,46-38W)•MAM season

Saravanan & Chang (2000), [3]Saravanan & Chang (2000), [3]• MAM Precip regression (a) NINO3 (b)NTA SST index

(4N-20N, approx 15W-78W)